A. Field of the Invention
This invention relates to the operation of a data network which interconnects different application modules, and more particularly relates to a method and apparatus for powering components on a data network.
B. Description of Related Art
Networks are the means through which commercially-available components or modules, such as computers, may communicate. One of the problems in formulating a network is the means through which power is supplied to the components in the network. The means for power must be reliable to guarantee network operation, accounting for disruptions to the power supply both at a component level and at a network level. When disruptions do occur, the goal is to maintain network operation and prevent loss of data. The means for power must also must comply with the standards of the particular network.
One such standard for a network is the IEEE 1394-1995 protocol (IEEE 1394) which is discussed in an article entitled "IEEE Standard for a High Performance Serial Bus" published by the IEEE. The IEEE 1394 is also referred to in the industry as Firewire.TM.. However, there are several problems when integrating the IEEE 1394 standard in the design of a multiple-module network. For example, the IEEE 1394 standard requires that the physical interface devices which interconnect with the IEEE 1394 bus powered by a galvanically-isolated supply voltage. With only one module supplying network power, and a large number of modules consuming network power, the 1.5 Ampere current sourcing limit imposed by the IEEE 1394 standard (based upon the connector design) is inadequate to supply power to all of the modules.
If one attempts to address the problem by requiring each module to supply its own power only, one looses the ability of the entire network to stay alive in the event of a power failure of a single module, if that module is being used as a network repeater. Further, if the modules are designed as power sources and power loads simultaneously, and the full IEEE 1394 voltage range of 8-40 Volts for power sources is used, it is difficult to determine which module will supply power to another module in the event of the power failure of one or more modules, and hence cannot guarantee reliable network operation. The present invention solves these and other difficulties.